Problem: Khan.scratchpad.disable(); William sells magazine subscriptions and earns $$10$ for every new subscriber he signs up. William also earns a $$21$ weekly bonus regardless of how many magazine subscriptions he sells. If William wants to earn at least $$72$ this week, what is the minimum number of subscriptions he needs to sell?
Answer: To solve this, let's set up an expression to show how much money William will make. Amount earned this week $=$ $ $ Subscriptions sold $\times$ Price per subscription $+$ Weekly bonus Since William wants to make at least $$72$ this week, we can turn this into an inequality. Amount earned this week $\geq $72$ Subscriptions sold $\times$ Price per subscription $+$ Weekly bonus $\geq $72$ We are solving for the number of subscriptions sold, so let subscriptions sold be represented by the variable $x$ We can now plug in: $x \cdot $10 + $21 \geq $72$ $ x \cdot $10 \geq $72 - $21 $ $ x \cdot $10 \geq $51 $ $x \geq \dfrac{51}{10} \approx 5.10$ Since William cannot sell parts of subscriptions, we round $5.10$ up to $6$ William must sell at least 6 subscriptions this week.